1. Field of the Invention
The present invention relates to a toner binder resin used for the development of electrostatic charge images or magnetic latent images in electrophotographic methods, electrostatic recording methods, and electrostatic printing methods, for example, and to a process for its production. The toner binder resin of the present invention has, in particular, a low odor and excellent charging stability.
2. Description of the Background
A typical image-forming process in electrophotographic methods and electrostatic printing methods entails: i) a photoconductive insulating layer is uniformly charged in a developing step, ii) the insulating layer is exposed to light, iii) the charge on the exposed sections is then dissipated to form an electrical latent image, iv) a charged fine powder toner is adhered to the latent image for visualization, v) the obtained visible image is transferred to a transfer material, such as transfer paper, and vi) heat or pressure is used for permanent fixing in a fixing step.
The toner and the toner binder resin used for the electrophotographic method or electrostatic printing method must exhibit various degrees of performance for each of these steps. For example, for adhesion of the toner to the electrical latent image in the developing step, the toner and the toner binder resin must hold a charge suitable for copy machines without being affected by the surrounding environment, including, for example, such as the temperature and humidity. Also, in the fixing step with a hot roller fixing system, it is essential to have a satisfactory non-offset property to avoid adhesion onto the hot roller and a satisfactory fixing property onto the paper. In addition, the toner must have blocking resistance to avoid blocking while being stored in the copy machine.
For copy machines, printers, or facsimiles, for example, used for electrophotographic methods, electrostatic recording methods and electrostatic printing methods, a hot roller is usually used, at a temperature of about 100-230xc2x0 C., for fixing the toner onto the paper. In this fixing step, multiple sheets are generally fixed one after another, and the toner accumulates on the hot roller in trace amounts that do not affect the non-offset property. The temperature of the hot roller increases because of continuous rotation or continuous sheet feeding, and heating of the toner accumulated on the hot roller causes volatilization of residual monomers and residual solvent present in the toner, thus producing an odor. In recent years, with the increased application of electrophotographic methods, the popularity of copy machines, printers and facsimiles has grown and their use in closed-in offices and homes has increased. Accordingly, there has been a demand for reduced odors during image formation and image fixing, as well as a strong demand for odor reduction even for toner production where the binder resin and other additives are kneaded with a kneader, or extruder, for example.
In the past, styrene-acrylic copolymers have been often used as toner binder resins and, because the problem of odor is caused by residual monomers and residual solvent in the toner binder resin, efforts have been made to reduce the residual monomer and residual solvent in the binder resin.
For reduction of the residual monomers and residual solvent in the binder resin, there have been proposed methods, such as one for achieving low odor by heating the polymerized resin to a temperature above its glass transition temperature and distilling off a prescribed amount of moisture to reduce the residual monomers, as described in Japanese Unexamined Patent Publication No. 1-70765, for example. In Japanese Unexamined Patent Publication No. 7-104514 and Japanese Unexamined Patent Publication No. 8-41123 as well, there are proposed methods of suppressing odor by reducing the volatile components, such as residual monomers and residual solvent. Japanese Unexamined Patent Publication No. 3- 101745 and Japanese Unexamined Patent Publication No. 3-101746 also propose methods designed to minimize odor by reducing the benzaldehyde contained in the toner binder resin.
However, although the method described in Japanese Unexamined Patent Publication No. 1-70765 allows efficient reduction of the volatile components with a boiling point of under 150xc2x0 C., removal of the volatile components of higher boiling points is difficult, and, therefore, it has not been possible to achieve adequate odor reduction. In methods which distill off prescribed amounts of moisture, the processing stability sometimes undergoes extreme deterioration, and the content of resin particles with a particle size exceeding 1,000 xcexcm sometimes reaches about 5%, thus leading to the problem of a reduced charging property of the toner. The methods described in Japanese Unexamined Patent Publication No. 1-70765, No. 7-104514 and No. 8-41123 merely reduce the monomers and solvents remaining in the resin after polymerization, and are not particularly concerned with the other volatile components that cause odors. Consequently, adequate odor reduction has yet to be achieved. Moreover, even the methods described in Japanese Unexamined Patent Publication No. 3-101745 and No. 3-101746, while achieving reduction in benzaldehyde, do not succeed in satisfactorily removing the other volatile components and have therefore not achieved adequate odor reduction.
Accordingly, it is an object of the present invention to provide a toner binder resin with low odor and excellent charging stability as a toner, as well as a process for its production.
It is, in particular, an object of the present invention to provide a toner binder resin, containing a styrene-acrylic copolymer or a mixture thereof, wherein the total content of volatile components is no greater than about 1,500 ppm, the content of volatile components with benzene rings is no greater than about 1,400 ppm, and the content of volatile components with benzene rings and a boiling point of below 200xc2x0 C. is no greater than about 500 ppm.